Amplifying system



June 27, 1933. THOMPSON 1,915,629

AMPLIFYING SYSTEM Filed Dec. 26, 1928 NVENTOR Z 2'11 c0121 Thompson Patented June 27, 1933 STATES rare orric LINCOLN THOMPSON, or NAUGA'IUGK, oormnorrcnr, Assrenon TO RADIO GORPORA- 'rIoN or AMERICA, or NEW YORK, N. A CORPORATION or DELAWARE AMPLIFYING SYSTEM Application filed December 26, 1928. Serial No. 328,350.

This invention relates to audion vacuum tube amplification systems, and more part1cularly to a system adapted for use in amplifying detected signals from radio transmitters, electrically-operated phonographs, etc.

One object of this invention is to provlde an amplifying system of the above nature which will produce a high degree of amplification of signal volume without material disre tortion.

A further object is to provide a system of the above nature which will be simple in construction, inexpensive to manufacture, easy to install and manipulate, fool-proof, compact, and very efficient and durable in use.

With these and other objects in view there have been illustrated on the accompanying drawing two circuits in which the invention may be conveniently embodied in practice.

Fig. 1 represents a diagrammatlc view of a simple two-stage amplifying system embodying the present invention. N

Fig. 2 is a diagrammatic view showlng the application of the invention to a three-stage amplifier for an electrical phonographic pick-up, the amplified signals being combined in a single output transformer.

In the amplification of alternating electrical vibrations such as radio waves and the like, it has been customary in the past to employ an audion circuit having a negative potential on the grid in order to prevent the fiow of an appreciable electronic current bet tween the grid and the filament and the d1stortion usually consequent thereto. The input grid circuit of the audion was thus made practically electro-static.

By means of the present lnventlon an 1m proved amplification system has been provided in which no negative potential need be imposed upon the grid. The resistance in the input grid circuit is thus very materially reduced from that ordinarily employed, and the principal feature of the present invention is the provision of means for preventing distortion of the output signals, while at the same time permitting a relatively large current to flow in the rid filament circuit.

It is possible by means of the present invention to use tubes having an amplification constant of over four times that of the tubes usually used in previous conventional amplifying systems with the same undistorted power output.

The general theory of operation is as follows:

When a signal is applied to the grid circuit of an audion by means of a conventional transformer, for example, electrons will flow from the filament to the grid only when the signal potential is such as to make the grid more positive than the filament. The flow of current in the grid filament circuit loads the secondary of the coupling transformer which in turn loads the primary, tending to cause a drop in voltage in the input signal. No current, however, will flow when the grid is negative with respectto the lament. Consequently, the applied signal will be subjected to a load during the period when the grid is positive with respect to the filament, but no load will be put upon it when the grid is negative. These conditions will tend to react on the signal source in such a manner as to decrease the voltage thereof when the load occurs, but at other times the voltage of the incoming signal will remain normal.

To prevent distortion it is ordinarily necessary to employ an initial negative potential between the grid and filament. If a zero potential is applied between the grid and filament, under ordinary conditions, the distortion will be very severe because of the fact that the positive pulsations of the ap plied signal are subjected to a reacting load while the negative pulsations are subject to no load at all. Bymeans of the present invention it is unnecessary to employ a negative potential between the grid and filament but distortion is eliminated by applying the input signals to a pair of alternately-reaeting amplifying audion circuits in such .a manner thateven though both audions are operated at Zero difference ofpo-tential between the grid and filament, the load reacting on the signal source will be maintained substantially constant at any instant irrespective of whether the applied signal renders the grid" more positive or more negative than the filament.

The loss of amplification due to the energy consumed in the grid-filamentcircuit of the new system is more than compensated by the great increase of amplification occurring within the tubes themselves. 1

Referring now to the drawing in which like reference numerals denote corresponding parts throughout the several views, the numeral indicates the primary winding of an input transformer 10a fed by a detector tube of a radio set, an electrical phonograph pickup, or other source of signals. The energy received from the primary winding 10 leaves the transformed through the secondary winding llrwhich forms part of the grid-filament circuit of an audion 12 forming the first stage of amplification. The grid-filament circuit of the audion12 comprises a conducting wire 13, a grid 14, a filament 15, conducting wires 16and 17, and the secondary 11. The filament is in series with the wire 16, an A-battery 18, and a resistance 18a.

Voltage is supplied to the plate 19 of the audion .12 by means of a B-battery 20 connected at one terminal, as by a wire 21, to the wire 16, the other terminal of said B-battery 20 being connected by a wire 22 to a primary winding 23 of a transformer 24,-said primary 23 being connected tothe plate 19, as by a wire 25.

The secondary 26 of the transformer 24 is adapted to transfer the amplified signal received from the primary 23 to the grid circuit of an audion 12a forming part of the second stage of amplification, and since the potential across the secondary 26 is 180 degrees out of phase with the potential across the primary 23, it willbe seen that at any instant when the voltage drop across the primary 23 is positive, that across the secondary will be negative. The amplified signals from the secondary 26' are thus caused to pass through the wire 27, grid 28, filament 29, and wires 30 and 31, back to the secondary 26. Y

The amplified oscillations from the audion 12a are converted into audible sound waves by means of a loud-speaker, not shown, adapted to be connected to binding posts 32 located in the plate circuit of said audion 12a, said plate circuit comprising a plate 33,- wire 34, wire 35, B-battery 36, wires 37 and 38, wires 39 and 40, wire 30, and the filament 29. It will be understood of course that a telephone receiver or other receiving instrument may .be substituted for the loud speaker withinthe spirit of the invention.

The filament 29 is supplied with energy for heating it-toincandescence by means of an A-battery. 41, the negative terminal of which is connected to the wire 40 and hav-* ing its positiveterminal connectedby a wire 42 to a resistance 43 which. in turn is connected by awire 44 to said filament 29.

Theamplified signals from the first stagc of amplification are also transmitted from the plate 19 of the tube 12 by means of a conducting wire 45 to the grid 46 of a third audion 12b. The grid filament circuit of the audion 12?) comprises the wire 45, the grid 46, the filament 47, a wire 48, wires 49, and 38, wire 50, wire 22, and the primary winding 23.

The amplified output signals from the audion 121) are delivered to a loud-speaker, not shown, connected by binding posts 51 in series with the plate 52, wire 53, wire 54, B-battery 55, wire 56, and the wire 48. The current for heating the filament 47 is obtained from an A-battery 57 connected to the wire 48 at one terminal, and at its other terminal to a wire 58 leading to a resistance 59, the latter being connected by a wire 60 to the filament 47. I It will be seen that the amplified signals are applied to both the audions 12a and 12?), the audion 12a receiving its signal input from the secondary 26 of the transformer 24, whereas the audion 126 receives its signal input from the voltage drop across the primary 23 of said transformer 24. The windin gs are preferably so adjusted and connected to the audions that at the instant when the grid ofthe audion 12a is positive with respect to its filament, the grid of the audion 126 will be negative with respect to its filament, and vice versa. Consequently,when the grid 28 of the tube 12a is positive, electronic current will flow in the grid-filamen circuit of said tube, thus reacting upon and loading the secondary 26 of the transformer 24 which in turn will load the primary 23 of said transformer and also the plate circuit of the tube 12. \Vhen the grid of the tube 12a is negative, it will not react upon the transformer secondary 26 as there will then be no electronic flow, but since, as above stated, the grid 46 of the tube 125 will at that instant be positive, the primary 23 of the transformer 24 and the plate circuit of the tube 12 will again be loaded by reaction from the grid circuit of the tube 126.

1 It is evident from the above that by properly proportioning the transformer 24 and employing tubes 12a and 12b of suitable and similarcharacteristics, the effect of the load produced by the combined grid circuits of the tubes 12a and 12?) will be substantially constant for equal positive or negative voltages. Consequently, both the positive and negative portions of the signal will be amplified alike.

It will be understood that the tubes 12a and 12?; may be so chosen that the grid currentgrid voltage characteristic curves will be substantially lineal for positive grid potentials, and thus the load due to the grid circuits of said tubes will be substantially equivalent to a constant resistance within the overload limits.

t will be also understood that while the second stage of amplification has been embodied in a pair of audion tubes 12a and 12?) by way of example, any rectifying devices may be substituted for either of said tubes whose voltage-current characteristic curve matches the grid-current, grid-voltage characteristic curve of said substituted tube.

It will also be understood that while in Fig. 1 the input signals are supplied to the pair of alternately reacting audions 12a and 126 by an audion 12 of a preceding stage, it is within the spirit and scope of the present invention to employ any other desired source of signals to be applied to the primary winding 23 of the transformer 24.

One advantage of the present invention is that it is quite economical of batteries for the reason that the same filament and plate batteries may be used tosupply all three of the tubes 12, 12a, and 12?). although for simplicity of explanation, three separate A-batteries and three separate B-batteries have been herein shown.

It will also be understood that all conditions must be so adjusted as to control the source of the input signal in such a manner as to keep it below overloading conditions.

The tubes 12a and 127) have, as previously explained, very high amplification constants as compared to tubes used in the circuits in ordinary usage. Consequently, they have a very long straight line portion of the grid voltage-plate current characteristic curve for positivegrid voltages, and hence with this system of amplification unusually large positive pulsations of signals may be handled without material distortion. Although the negative pulsations have a much lower overload limit, the arrangement is such that at any instant when one of the tubes handles a negative pulsation, the other tube handles the signal as a positive pulsation and even though such negative pulsation may be somewhat distorted when its overload limit is reached, the simultaneous positive pulsation will not be distorted within its higher overload limit. This semi-distortion will not generally be noticed by the ear of the listener, or at least it will be much less noticeable than when both positive and negative pulsations are distorted.

In the modified form of the invention shown in Fig. 2, a threestage amplifier is disclosed in which signals are supplied by an electrical phonographic pick-up 61 provided with a suitable adjustable controlling potentiometer 62 in shunt therewith. Moreover, in this modification, instead of having a pair of outputloud-speakers, each delivering onehalf of the signal volume, the output signals are combined in a single transformer f0 operating a single loud-speaker.

As clearly shown in Fig. 2, the input signals from the electrical pickup 61 are impressed upon an audion 60a of the first stage of amplification by arranging said pickup 61 in series with a wire 63, the potentiometer 62, an adjustable tap wire 64', wire. 65, grid 66, filament 67, wire 68, wire 69, and a wire 70, connected to said pickup 61. The lower terminal of the potentiometer 62 is connected to said wire 69 as shown.

In order to couple the first stage of amplification to the second stage, the plate 71 of the audion 60a is connected by wires 72 and 73 to a condenser 74:, the latter being joined to a wire 75, connected at a junction point 76 to a pair of wires 7 7 and 80. The signals will pass through the wire 77 to the grid 78 of an audion 79. The signals will also pass from the junction point 7 6 through a wire to the primary 81 of a coupling transformer 82. The signals impressed upon the audion 79 will pass through the grid 78 to the filament 83, the grid circuit of said audion 79 being completed by way of wires 841, 90, 91, the primary 81, and wire 80 connected tothe junction 76 to the wire 77. The signals impressed upon the primary 81 of the transformer 82 will pass from the secondary 86 of said transformer through wire 87 to the grid 88 of an audion 7 9a, and after passing through the filament 89 will return to said secondary 86 through wires 90 and 91.

The signals. amplified in the audions 79 and 79a are delivered to audions 92 and 92a of the third stage of amplification by means of an arrangement of circuits similar to those of the second stage of amplification. Thus, from the plate 93 ofthe audion 79 the signals pass through a wire 94, condenser 95, wire 96, to a junction point 97 where the signal energy flows through wire 98 to the grid 99 of an audion 92. The grid circuit of the tube 92 is completed by a choke coil 100 connected to the filament 111 by the wire 101.

The plate 103 of the audion 79a is also connected through wires 104 and 105, a condenser 106, and wire 107, to the primary 107 a of the transformer 102. It will be readily seen that the amplified signals from the audion 7 9a are adapted to fiow through the transformer 102, and be transmitted by the secondary108 to the grid 109 of the audion 92a, the grid circuit thereof being completed by the filament 110 and wire 111a connected to the secondary 108. It will thus be seen that the grid circuits of the audions 92 and 92a will alternately receive signal impulses of opposite phase.

The combined output signals from the tubes 92 and 92a are adapted to be joined in a single output transformer 116 having a primary 117 and a secondary 118. The primary 117 is connected by a wire 119 to the plate 120 of the audion 92 and by a wire 121 to a plate 122 of the tube 92a. The joint plate circuit is completed by a wire 123 con.- nectingthe filaments 110 and 111. current is supplied to the primary 117 by a Plate 124 connected to respective filaments of said audions by suitable wiring and resistances, as shown in Fig. 2. Similarly, B-battery voltage is supplied to the plate circuits of each of said audions by means of a B-bat:

an tery 125 connect-ed to the filaments and plates of the respective a'udionsby suitable wiring as shown. In order to insulate the transformers 82 and 102 from the .B-battery voltage, provision is made of suitable choke coils 126 and 127.

Since the operation of the amplifying system shown in Fig. 2 is quite similar to that shown in Fig. 1, furtherdescription thereof is deemed to be unnecessary.

m While there-have been disclosed in this specification two forms in which the invention may be embodied, it is to be understood that these forms are shown for the purpose of illustration only, and that the invention is not to be limited to the specific disclosures but may be modified and embodied in various other forms without departing from its spirit. In short, the invention includes all the modifications and embodiments coming in within the scope of the following claims.

Having thus fully described the invention, what is claimed as new and for which it is desired to secure Letters Patent is:

1. In an amplifying system, an audion n v a having a grid clrcuitand a plate circuit, said id circuit adapted to receive a supply of alternating electrical vibrations, said plate circuit including-the primary of a coupling transformer, the secondary of said transformer being in the grid circuit of a second audion, the primary of said transformer being in the grid circuit of a third audion, and means in the plate circuits of said second and third audions for rendering audible $5 the amplified signals from both of said audions.

2. In an amplifying system, a source of alternating electrical vibrations, said source including the primary of a coupling transm former, the secondary of saidtransformer being in the grid circuit of an audion, the primary of said transformer being in the grid circuit of a second audion, and means in the a plate circuits of said audions for rendering audible the amplified signals from both of said audions.

3. In an audion amplifying system, a source of alternating electrical vibrations, a

pair of audions, said source being transformer-coupled to the grid circuit of one of said audions, the primary of said transformer being in the grid circuit of the second of said audions, and means in'the plate circuits of said audions for rendering audible the ainplified signals from both of said audions.

4. In an amplifying system, a source of alternating electrical vibrations, said source including theprimary of a coupling transformer, the secondary of said transformer being in the grid circuit of an audion, the

primary of said transformer being in the grid circuit of a second audion, and means in the plate circuits of said audions for combining and rendering audible the amplified signals from both of said audions.

5. In an audion amplifying system, a source of input energy, a transformer, a pair of audions, the secondary of said transformer being in series with the grid circuit of one of said audions, a second stage of amplification, the primary of said transformer being connected in the circuit with the grid circuit of the second audion, means for com bining the amplified output of the two audions, and means for rendering said combined output audible.

6. In an audion amplifying system, a source of input energy, said source being transformer-coupled to the grid circuit of an audion, the primary of said transformer being connected with the grid circuit of a second audion, means for combining the amplified output of the two audions, and means for rendering said combined output audible.

7. In an audion amplifying system, a source of alternating electrical vibrations, a pair of alternately reacting audions, means for operating the grid filament circuits of said audions on a zero or positive bias, means for reversing the phase of said vibrations, and means for applying the original phase vibrations to one of said audions and the reversed phase vibrations to the other of said audions whereby the reacting load on said source will be rendered substantially equivalent to a pure resistance, the cathodes of said audions being directly connected together.

8. In an audion amplifying system, a source of alternating electrical vibrations, a pair of alternately reacting audions, one of said audions being directly coupled to said source and the other of said audions being coupled to said source'by an independent im pedance circuit having a phase potential op-' posite to that of said source, and means in the plate circuits of said audions for rendering audible the amplified signals from both of said audions, and means to operate said audions so that the sum of the grid currents in both audions at all times will bear a substantially linear relation to the voltage of the applied vibrations. i

9. In an audion amplifying system, a.

source of alternating electrical vibrations, a pair of alternately reacting audions, one of said audions being directly coupled to said source and the other of said audions being coupled to said source by a choke coil circuit having a phase potential opposite to that of said source, and means in the plate circuits of said audions for rendering audible the amplified signals from both of said audions.

10. In an audion amplfying system, a source of electric Waves, a pair of matched alternately reacting audions, means for causing each of said audions to operate under conditions which cause appreciable electron currents to flow in the grid circuits thereof,and means for causing the grid circuits of each audion to react on said source on such a manner that their joint reaction is similar to that of a pure resistance.

11. In an audion amplifying system, a source of electrical Vibrations, a pair of matched alternately reacting audions, one of said audions being directly coupled to said source, and the other of said audions being coupled to said source in reversed phase potential relation, and means for operating said audions to cause the load reacting on said source to be substantially constant at all times.

12. In an audion amplfying system, an audion having a grid circuit and a plate circuit, said grid circuit adapted to receive a supply of alternating electrical vibrations, said plate circuit including the primary of a coupling transformer, "the secondary of said transformer being in the grid circuit of a second audion, the primary of said transformer being in the grid circuit of a third audion, and means in the plate circuits of said second and third audions for receiving the amplified signals from both of said audions.

13. In an audion amplifying system, a source of alternating electrical vibrations, said source including the primary of a coupling transformer, the secondary of said transformer being in the grid circuit of an audion, the primary of said transformer bemg 111 the grid circuit of a second audion,

and means in the plate circuits of said audions for combining the amplified signals from both of said audions.

14. In an audion amplfying system, a source of alternating electrical vibrations, a pair of alternating reacting audions, one of said audions being directly coupled to said source and the other of said audions being coupled to said source by an independent impedance circuit having a phase potential opposite to that of said source, and means to operate said audions so that the sum of the grid currents in both audions Will bear substantially a linear relation to the voltage of the applied vibrations.

15. In an audion amplifying system, a source of electrical Vibrations, a pair matched alternately reacting audions, means for causing each of said audions to operate under conditions Which cause appreciable electron currents to flow in the grid circuits thereof, and means for operating said audions to cause the load reacting on said source to be substantially constant.

16. In an audion amplifying system, a source of electrical vibrations, a pair of alternately reacting audions coupled thereto, means for causing each of said audions to operate under conditions which cause appreciable electron currents to flow in the grid circuits thereof in response to said electrical vibrations, and means for operating said audions to cause the load reacting on said source to be substantially constant, said means providing a low impedance grid circuit for each of said audions.

In testimony whereof, I have afiixed my signature to this specification.

LINCOLN THOMPSON. 

